In this sector, the use is known of systems for monitoring the therapeutic beam, associated with the system for distribution of the dose of the machines for hadron therapy, for the measurement in real time of the flux of particles, of the position and of the profile of the beam in the plane transverse to the direction of propagation of the same beam. For reasons of safety, these monitoring systems are disposed in the immediate vicinity of the patient and make the measurement in a redundant, independent, fashion and lead to a minimum interference on the beam itself. These systems do not however measure the energy of the particles of the beam; they are limited to measuring its position and its profile, in the plane perpendicular to the propagation, whereas the flux is determined indirectly through the measurement of the electric charge produced by ionization in the gas of suitable ionization chambers and via a dosimetric calibration of the said chambers to be periodically carried out through measurements of doses in suitable dummy systems, with certified dosimetries, at the various energies of the beam.
Generally speaking, the energy of the particles of the beam is regulated by fixing the energy of extraction of the beam from the source (particle accelerator) via a suitable configuration of the accelerator, or by controlling appropriate equipment provided along the line of propagation of the beam in order to modulate the energy of the latter. The energy of the particles is thus a pre-defined parameter of the system for production of the beam. The need is however pointed out to integrate into the monitoring system previously described an independent measurement of the energy of the particles of the beam, in order to allow a greater safety in hadron therapy treatments.
This need arises from the new requirements, having come to the fore in the medical field and in the process of being defined in international standards, for guaranteeing to the patient an even higher margin of safety on the exact depth of penetration of the beam into tissues, determined by the energy of the particles, and on the number of particles delivered during the irradiation. For this purpose, the presence is required of at least two independent monitoring systems, each one being capable of measuring the number of particles passing through it and their mean energy, with the capability of interrupting the treatment if these values do not correspond to those required in the planning phase of the treatment.
Specifically, the clinical requirements are to guarantee in real time, during the execution of the treatment and for each beam directed onto the patient, an experimental uncertainty on the depth into the tissue at which the dose is deposited of less than 1 mm (corresponding to the uncertainty in the position of the interface between healthy tissue and tumor-infected tissue to be treated), and an uncertainty on the dose of radiation released equal to or less than 1%.
The need for a new system for monitoring the beams is further reinforced by the observation that the prior art does not allow a simultaneous measurement in real time and in a non-destructive manner of both the energy and of the number of particles delivered by a hadron beam with a precision on the number of particles and on their mean energy so as to guarantee the clinical requirements previously described.
The publication “Design and characterization of the beam monitor detectors of the Italian National Center for Oncological Hadron-therapy (CNAO)” by S. Giordanengo et al. (Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment, vol. 698, pages 202-207, XP028958886) describes a system for measuring a mono-energetic hadron beam, comprising a first detection unit which supplies a particle count and a second detection unit which supplies an output signal proportional to the total charge delivered by the beam.
The publication “Diamond detectors for the monitoring of carbon-ion therapy beams” by M. Rebisz-Pomorska et al. (Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment, Elsevier BV North-Holland, NL, vol. 620, no. 2-3, pages 534-539, XP027143627) describes a system comprising a single diamond detector designed to measure the number of particles and the energy of the beam in real time.